Use even rounding for better results when converting from scalar to fdot6

src/core/SkEdge.cpp

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkEdge.h"
@@ skipping 18 matching lines @@
     return value << (16 - 6 - 1);
 }
 
 /////////////////////////////////////////////////////////////////////////
 
 int SkEdge::setLine(const SkPoint& p0, const SkPoint& p1, const SkIRect* clip,
                     int shift) {
     SkFDot6 x0, y0, x1, y1;
 
     {
+#ifdef SK_RASTERIZE_EVEN_ROUNDING
+        x0 = SkScalarRoundToFDot6(p0.fX, shift);
+        y0 = SkScalarRoundToFDot6(p0.fY, shift);
+        x1 = SkScalarRoundToFDot6(p1.fX, shift);
+        y1 = SkScalarRoundToFDot6(p1.fY, shift);
+#else
         float scale = float(1 << (shift + 6));
         x0 = int(p0.fX * scale);
         y0 = int(p0.fY * scale);
         x1 = int(p1.fX * scale);
         y1 = int(p1.fY * scale);
+#endif
     }
 
     int winding = 1;
 
     if (y0 > y1) {
         SkTSwap(x0, x1);
         SkTSwap(y0, y1);
         winding = -1;
     }
 
@@ skipping 110 matching lines @@
 
     // each subdivision (shift value) cuts this dist (error) by 1/4
     return (32 - SkCLZ(dist)) >> 1;
 }
 
 int SkQuadraticEdge::setQuadratic(const SkPoint pts[3], int shift)
 {
     SkFDot6 x0, y0, x1, y1, x2, y2;
 
     {
+#ifdef SK_RASTERIZE_EVEN_ROUNDING
+        x0 = SkScalarRoundToFDot6(pts[0].fX, shift);
+        y0 = SkScalarRoundToFDot6(pts[0].fY, shift);
+        x1 = SkScalarRoundToFDot6(pts[1].fX, shift);
+        y1 = SkScalarRoundToFDot6(pts[1].fY, shift);
+        x2 = SkScalarRoundToFDot6(pts[2].fX, shift);
+        y2 = SkScalarRoundToFDot6(pts[2].fY, shift);
+#else
         float scale = float(1 << (shift + 6));
         x0 = int(pts[0].fX * scale);
         y0 = int(pts[0].fY * scale);
         x1 = int(pts[1].fX * scale);
         y1 = int(pts[1].fY * scale);
         x2 = int(pts[2].fX * scale);
         y2 = int(pts[2].fY * scale);
+#endif
     }
 
     int winding = 1;
     if (y0 > y2)
     {
         SkTSwap(x0, x2);
         SkTSwap(y0, y2);
         winding = -1;
     }
     SkASSERT(y0 <= y1 && y1 <= y2);
@@ skipping 123 matching lines @@
     SkFDot6 twoThird = (a + 6*b - ((c << 4) - c) + (d << 3)) * 19 >> 9;
 
     return SkMax32(SkAbs32(oneThird), SkAbs32(twoThird));
 }
 
 int SkCubicEdge::setCubic(const SkPoint pts[4], const SkIRect* clip, int shift)
 {
     SkFDot6 x0, y0, x1, y1, x2, y2, x3, y3;
 
     {
+#ifdef SK_RASTERIZE_EVEN_ROUNDING
+        x0 = SkScalarRoundToFDot6(pts[0].fX, shift);
+        y0 = SkScalarRoundToFDot6(pts[0].fY, shift);
+        x1 = SkScalarRoundToFDot6(pts[1].fX, shift);
+        y1 = SkScalarRoundToFDot6(pts[1].fY, shift);
+        x2 = SkScalarRoundToFDot6(pts[2].fX, shift);
+        y2 = SkScalarRoundToFDot6(pts[2].fY, shift);
+        x3 = SkScalarRoundToFDot6(pts[3].fX, shift);
+        y3 = SkScalarRoundToFDot6(pts[3].fY, shift);
+#else
         float scale = float(1 << (shift + 6));
         x0 = int(pts[0].fX * scale);
         y0 = int(pts[0].fY * scale);
         x1 = int(pts[1].fX * scale);
         y1 = int(pts[1].fY * scale);
         x2 = int(pts[2].fX * scale);
         y2 = int(pts[2].fY * scale);
         x3 = int(pts[3].fX * scale);
         y3 = int(pts[3].fY * scale);
+#endif
     }
 
     int winding = 1;
     if (y0 > y3)
     {
         SkTSwap(x0, x3);
         SkTSwap(x1, x2);
         SkTSwap(y0, y3);
         SkTSwap(y1, y2);
         winding = -1;
@@ skipping 115 matching lines @@
         success = this->updateLine(oldx, oldy, newx, newy);
         oldx = newx;
         oldy = newy;
     } while (count < 0 && !success);
 
     fCx         = newx;
     fCy         = newy;
     fCurveCount = SkToS8(count);
     return success;
 }